In an electrophotographic image forming apparatus such as a laser printer, an electrostatic copying machine, a plain paper facsimile machine or a printer-copier-facsimile multifunction machine, a charging roller is used for uniformly electrically charging a surface of a photoreceptor body.
The charging roller typically includes a roller body having a single layer structure or a multilayer structure including a layer produced, for example, by forming a semiconductive rubber composition into a tubular body and then crosslinking a rubber of the rubber composition.
Incidentally, fine particles such as external additive particles externally added to toner or finely broken toner particles occurring when image formation is repeated are liable to adhere to and accumulate on an outer peripheral surface of the roller body, thereby causing imaging failure. For suppression of the imaging failure, it is a general practice to condition the outer peripheral surface, for example, by polishing the outer peripheral surface and/or coating the outer peripheral surface with a coating film after the polishing.
However, the coating film is formed by applying a liquid coating agent onto the outer peripheral surface of the roller body by a spraying method, a dipping method or other coating method, and then drying the applied liquid coating agent. Therefore, the coating film is liable to suffer from contamination with foreign matter such as dust in the formation thereof, uneven thickness and other defects.
For preparation of the coating agent, an organic solvent is required. The use of the organic solvent may exert a great load on the environment, and go against a recent trend toward reduction of VOC (volatile organic compounds).
It is also contemplated that various asperities which are supposed to prevent the adhesion and the accumulation of the fine particles are formed on the outer peripheral surface of the roller body, for example, by polishing the outer peripheral surface under properly controlled polishing conditions or processing the outer peripheral surface by a laser processing method, a blasting method or other processing method, rather than forming the coating film (see Patent Documents 1 to 4)